A book published in Italy is set to reignite a smouldering controversy over how close the Nazis came to manufacturing a nuclear device in the closing stages of World War II.

The author, Luigi Romersa, 88, is the last known witness to what he and some historians believe was the experimental detonation of a rudimentary weapon on an island in the Baltic in 1944.

Hitler's nuclear program has become a subject of intense dispute in recent months, particularly in Germany. An independent historian, Rainer Karlsch, met a barrage of hostility when he published a study containing evidence that the Nazis had got much further than previously believed.

On October 12, 1944, Romersa, then a 27-year-old war correspondent, was taken to the island of Rugen, where he watched the detonation of what his hosts called a "disintegration bomb".

"They took me to a concrete bunker with an aperture of exceptionally thick glass. There was a slight tremor in the bunker; a sudden, blinding flash, and then a thick cloud of smoke. It took the shape of a column and then that of a big flower.

"The officials there told me we had to remain in the bunker for several hours because of the effects of the bomb. When we eventually left, they made us put on a sort of coat and trousers which seemed to me to be made of asbestos and we went to the scene of the explosion.

"The effects were tragic. The trees around had been turned to carbon. No leaves. Nothing alive. There were some animals - sheep - in the area and they too had been burnt to cinders."

When he wrote of his experiences after the war, "everyone said I was mad". By then, it was universally accepted that Hitler's scientists had been years away from testing a nuclear device.

However, documents published recently by Mr Karlsch and a US scholar, Mark Walker, have punctured this consensus. Russian archives have shown one of the German scientists lodged a patent claim for a plutonium bomb as early as 1941 and, in June, the two historians published an article in Physics World that included what they said was the first diagram of one of the bombs Hitler's scientists were trying to build, a device that exploited both fission and fusion.